A laboratory culture system for pathological and physiological studies of rooted aquatic plants

Abstract

A biphasic system was designed for growing rooted Eurasian water milfoil, Myriophyllum spicatum L., to avoid artificial characteristics of flask culture. Aquaria (21 L) containing undergravel filters, air-lift pumps, 50-W heaters, and Plexiglas lids were sterilized in 70% ethanol and assembled aseptically. Plant shoots were rooted separately in polypropylene cups containing 60 g of artificial sediment approximating natural marl. The sediment provided over 90% of the nitrogen and phosphorus in the plants after 22 days growth. Plants were immersed in a mineral-salts medium with levels of nitrogen and phosphorus comparable with lake concentrations. Aeration was at 0.15 L ∙ min−1 and ranges of temperature and light intensity were from 17 to 32 °C and 30 to 250 μE ∙ m−2 ∙ s−1, respectively. The peak photosynthetic rate was 14 mg O2 ∙ g dry weight−1 ∙ h−1. The maximum specific growth rate, 0.14 mg ∙ mg−1 ∙ day−1, occurred at 27 °C and 250 μE ∙ m−2 ∙ s−1 and lasted for about 3 weeks before light became limiting. Bacterial density, ammonium nitrogen, soluble reactive phosphorus, and total phosphorus exhibited rapid changes during the first 12 days of the growth period, after which fluctuations diminished. The between-aquaria variance in shoot growth rate was insignificant (P > 0.70). When inorganic carbon in the liquid medium and phosphorus in the sediment were lowered from 2.86 to 1.14 mmol C ∙ L−1 and from 0.7 to 0.2 mg P ∙ g dry weight−1, milfoil growth was reduced by 47 and 74%, respectively. Control of the physiochemical environment, small variability, and high reproducibility make this a sensitive system for discerning various treatment effects, including those of pathogens.